Many synthetic polymers have been developed and used in processes for the recovery of natural resources. Generally a desirable property is that such polymers impart to a liquid an increased viscosity when a relatively small quantity of the polymer is added, and preferably at a minimal cost. There is an increasing demand for such polymers which will withstand hostile environments including, e.g. high temperatures, high salinity and high content of multivalent metal cations, commonly known as "hardness ions", as well as the high acidity, temperature and shear conditions encountered in processes such as acid fracturing.
It is also well known that undesirable water recovered from oil wells can result from the infiltration of naturally occurring subterranean water, or, in the case of waterflooding or steam flooding operations, from the injected drive water or steam. In both cases, water or steam flows through zones of high permeability to the producing well bores whereby oil in less permeable zones is bypassed. In water or steam flooding operations, the more permeable zones of subterranean formations tend to take most of the injected flood water or steam. While this is acceptable initially when the oil contained in the high permeability zones is being swept therefrom, it subsequently becomes undesirable as the oil in such zones becomes depleted. From that point on, the water or steam flood provides little benefit in enhancing oil production.
Methods and compositions for accomplishing near well and in depth plugging of high permeability zones by forming gels therein have been developed and used. The formation of the gels causes high permeability zones to be plugged or at least lowered in permeability whereby subsequently injected flood water or steam is caused to enter previously bypassed zones. This in turn causes the flood water or steam to mobilize increased amounts of oil which are recovered from the subterranean formation.
A variety of methods and polymer compositions which gel in situ to reduce the permeability of high permeability zones in subterranean formations have been utilized successfully for improving the sweep efficiency of water or steam flooding and/or reducing the production of naturally occurring formation waters, but such methods and compositions have generally been unsuccessful in applications requiring the formation of gels deep in high permeability zones having high temperatures, i.e., temperatures above about 160.degree. F. It would therefore be a significant contribution to the art to provide a polymer composition and a method for altering subterranean formation permeability at temperatures at 160.degree. F. and higher.
Polymers also have applications in well-treating fluids such as drilling fluids, completion fluids, work over fluids, stimulation fluids, and cement slurries which serve a number of functions. Drilling fluids cool the bit, bring the cuttings to the surface, and keep the oil, gas, and water confined to their respective formations during the drilling process. In addition, a highly important property of a drilling fluid is the ability to form an impervious layer upon the permeable walls of the borehole, which inhibits the ingress of water from the drilling fluid into the formation. Excessive water loss from the drilling fluids can cause severe problems. For example, filter cake buildup can become so thick that the drilling pipe may become stuck; also, there may be great difficulty in withdrawing the pipe from the hole. Further, high water losses can cause sloughing and caving in the shale formations.
A completion fluid is left behind the tubing in well completion for pressure control or corrosion prevention. This fluid should have the following desirable qualities: thermal stability, ease or re-entry for work over operations, and controlling formations. Because of the economics involved, the drilling fluid used to drill the well is also used as a completion fluid. If the drilling fluid is unsatisfactory to leave in the hole, a special fluid may be prepared.
In general, the well treating fluids usually are composed of fresh water or brine and solids suspensions and are fluids that are regulated at the well location by addition of viscosifiers, fluid loss control agents, salts, dispersants, lubricants, shale inhibitors, corrosion inhibitors, surface active agents, weighting materials, flocculants, and other additives of various kinds in accordance with the particular intended use.
A variety of polymer compositions have been utilized successfully as fluid loss control agent or as viscosifier to provide suspension of solids. However, none of these polymers has performed adequately in every situation. Therefore, it would be a valuable contribution to the art to provide a polymer composition which reduces fluid loss and provide suspension properties in hard brine environments.
Polymers also have applications in well treating fluids and waste water purification for removing undesired solids by "flocculation" of the solids. A number of polymers are being used as flocculants. It would be a useful contribution to the art if a polymer composition were provided that acts as a flocculant.